1. Field of the Invention
The present invention relates to an ink jet recording apparatus for performing recording by discharging ink from recording means to a recording medium.
2. Related Background Art
A recording apparatus such as a printer used as an output apparatus for a computer or, word processor, copying machine, or a facsimile apparatus is structured to record images by recording means on a recording sheet, thin plastic sheet, or other recording media in accordance with the image information. The aforesaid recording apparatuses are divided into those of an ink jet type, wire dot type, thermal type, laser beam type, and some others by the method that each apparatus employs for its recording.
Among these methods, the ink jet recording method (ink jet recording apparatus) is such that ink is caused to be discharged from recording means (recording head) onto a recording medium to perform a desired recording with the impacted ink dots thereon. Since the diameter of the ink dot discharged can be made extremely small, it is possible to record superfine images on an ordinary sheet at high speeds without any particular treatment. In addition, this is a non-impact method and there is less noise. With this method, there is an advantage that it is easy to record color images using a plurality of color inks. Particularly, the recording means (recording head) which utilizes thermal energy for discharging ink among those ink jet methods can be manufactured by the use of the semiconductor fabrication process such as etching, vapor deposition, sputtering, and the discharging ports required for discharging ink with a high density and the conductive ink passes connected thereto can be fabricated with ease.
However, as the discharging ports are arranged in such a high density, disabled ink discharging, deviation in the ink discharging orientations, or other discharging defectives tend to occur if paper particles, dusts, overly viscous ink, or the like adheres to the vicinity of the discharging ports of the aforesaid recording means or there are generated ink puddles or the like in the vicinity of the ink discharging ports. This results in degrading the image quality. Therefore, in the ink jet apparatus, there have been designed countermeasures such as means for removing various foreign matters adhering to the vicinity of the discharging ports which bring about inferior image quality.
For example, as means for preventing the clogging of the discharging ports due to the increased viscousity of ink resulting from the evaporation of the ink solvent or the adhesion of dust or the generation of bubbles, there have been proposed structures such as disclosed in U.S. Pat. No. 4,045,802 and U.S. Pat. No. 4,600,931 in which the discharging port formation surface of the recording head is covered by a cap when no recording is performed to protect the surface from being exposed to the atmosphere for the prevention of the dust adhesion as well as of the evaporation of the ink solvent, so that the discharging ports are maintained in a desirable condition, or a discharging recovery device is arranged to forcibly exhaust ink from the discharging ports together with the overly viscous ink, dust, bubbles, or the like in the discharging ports simultaneously by the use of a suction pump.
Also, there is a structure (hereinafter referred to as prior art 1) whereby dust and overly viscous ink in the vicinity of the discharging ports is removed by wiping the front face (discharging port formation surface) of the recording head by a plastic blade made of rubber and others as disclosed in U.S. Pat. No. 4,112,435, U.S. Pat. No. 4,364,065 or Japanese Patent Laid-Open Application 58-94472. Further, there is, for example, another structure (hereinafter referred to as prior art 2) that slides a brush and ink absorbent member in the circumference of the discharging ports in order to obtain the same effect as in the prior art 1 as disclosed in U.S. Pat. No. 4,306,245.
Nevertheless, after many experiments conducted by the inventor et al hereof, it has been discovered that in some cases the ink discharging defects cannot be recovered sufficiently by the techniques according to the prior arts 1 and 2 described above, and that there is still need for improvement.
In other words, in the case of the prior art 1, it is possible to remove the droplets having a comparatively low viscosity such as the ink droplets which have adhered to the circumference of the discharging ports or the dew condensation on the circumference of the discharging ports due to the increased humidity in the apparatus by the discharging recovery operation by suction and the like. However, when recording is resumed after a reset or suspension after a long period of time, it is noticed that the images are disturbed due to the ink droplets which do not adhere to the accurate positions on the surface of the recording sheet because, although there is no disabled ink discharging by the use of the discharging recovery device, it is still difficult to eliminate the deviation of the flying directions of the ink droplets.
Also, in the case of the prior art 2, the required cleaning is repeatedly operated at a home position, which in some cases brings about the surface staining or scuffing due to the durability of the ink absorbent, and it may result in the defective ink discharging because of the adhesion of foreign matters to the circumference of the discharging ports in spite of the intended cleaning.
Under the circumstances, the inventor et al hereof have conducted various trial recordings thoroughly as further experiments while carefully observing the circumference of the discharging ports in order to find out the causes for the generation of the ink discharging defects. As a result, it is found that the defects occur due to the changes in the state of ink adhering to the circumference of the discharging ports OF as shown in FIGS. 2A through 2D which illustrate the states of the discharging port surface of the recording head. In other words, as shown in FIGS. 2A and 2B, if the ink droplets ID adhere to the circumference of the discharging ports OF of the recording head 5 due to dew condensation or the like, these droplets are dried to create extremely thin ink films Id which are fixed to the circumference of the discharging ports OF as shown in FIG. 2C and FIG. 2D. Many of the ink films Id such as those shown here have been created when the performance of the recording is suspended for a long period of time.
Although it has been known that defective discharging results when recording is resumed after a long period of recording suspension, the increased viscosity of ink or air mixture is considered to be its cause. It was through that the clogging caused by the increased viscosity of ink and air mixture are the major causes for the defective discharging, but it has not been known that the deviation of the ink discharging orientation is caused by the above-mentioned ink film Id. Moreover, these ink films Id cause the ink repellency of the discharging port surface to be lowered thus creating the state where the ink droplets easily adhere thereto.
Taking these facts into account, the present inventor et al hereof have repeated many experiments and discussions on the structure of an ink jet recording apparatus capable of obtaining desirable recording images by removing the causes of the defective dischargings most effectively. As a result, it is also found that as means for cleaning the discharging port surface of an ink jet recording apparatus, it is still preferable to remove the ink droplets, ink puddles, and dew condensations on the vicinity of the discharging ports by the use of the aforesaid plastic blade in consideration of the wiping effect and durability.
However, when the ink droplets or ink puddles adhere for a long period of time and are dried to form the extremely thin films on the circumference of the discharging ports in a fixed state, the discharging orientations become unstable due to these ink films although there appear to be no ink puddles. In addition, the ink repellency of the discharging port surface is lowered so that the ink puddles tend to be created thereon. Accordingly, the spiral dischargings tend to occur. It is impossible to remove such an ink film as this sufficiently with the cleaning conducted by the aforesaid blade.
As a result of the ardent research and repeated experiments by the present inventor et al hereof for the purpose of improving the aforesaid technical problems, it has been recognized that the adhesive foreign matters can be removed desirably by a slidably rubbing member other than the blade which is slidably in contact with the discharging port surface with a predetermined timing. Particularly, a constant relationship between the adhesive conditions of the foreign matters and the heat temperatures and image formation column numbers should be found, and by performing the contact sliding with a predetermined timing which is selected by both of them, it is possible to effectuate a desirable cleaning of the discharging ports.